I remember in older version of InDesign there was a checkbox which is controlled exporting blank paragraphs (lines) to epub format - CC does it automatically without them... And i can't never find how to chenge it - is this even possible?

I think that retaining blank lines was possible in the first build (ID 8.0) in CS6. That caused lots of problems and was removed in an update. I don't think it's possible to retain blank lines. This is consistent with the way HTML usually works: All extra spaces and extra returns are removed in HTML.

You should accomplish this by adding space before and space after in your paragaph styles. This is correctly converted into the CSS and HTML.